Conventional concrete blocks have the advantages in construction of low material cost, durability, strength and simplicity. However, assembly into a useful wall requires considerable time, skill and almost continuous use of mortar. Workers must set each block on top of a bed of mortar, and then tap the block until the block is plumb, flush with the wall and at the correct height. Thus, block stacking is time-consuming and requires considerable training. Moreover, rain or subfreezing weather conditions can prevent proper curing of the mortar. Measures can be taken to allow construction in such weather conditions but can be economically unfeasible. As a result, work is usually suspended during adverse weather conditions.
Various attempts have been made to produce mortarless or dry-stack blocks where blocks are stacked to form walls with no intervening mortar in order to avoid the problems associated with the use of mortar. A problem with mortarless blocks is that conventional block making equipment cannot consistently manufacture blocks with height tolerances of less than 1/16 inch. In a block wall having a running bond pattern (each block resting on two blocks below), such height variations are too large for building stable mortarless walls. Typically, in conventional block walls, the mortar compensates for the height variations in the blocks. Most current mortarless blocks have designs which compensate for height variations but are either uneconomical to manufacture or require too much skill and time to assemble, thereby defeating the advantages of mortarless blocks.